1. Field of the Invention
This invention relates to regenerative incinerators for thermally oxidizing contaminated fumes and, more particularly, to incinerators which have means for purging contaminated fumes from their regenerators.
Incinerators are frequently employed to destroy harmful emissions resulting from various processes. Frequently, incinerators are used to oxidize light hydrocarbon emissions. For example, the finishing line on an aluminum strip coating process may emit toluene, which is directed with the finishing line exhaust to a downstream incinerator where toluene and other harmful emissions are oxidized at high temperatures. The incinerator exhaust is then suitable for introduction to the atmosphere, or it may be recycled to meet other plant energy needs. Incinerators are also applied in conjunction with food processing to control odors, pharmaceutical and fragrance manufacturing, painting and printing and many other applications.
Thermal regenerators, including beds of ceramic materials, may be included in the incinerator design. The regenerative beds greatly increase the overall thermal efficiency of the incinerator (as high as 95%), reducing annual fuel costs and maximizing contaminant destruction rates within the incinerator. The contaminated fumes are typically raised to temperatures of 1,200.degree. F. to 2,200.degree. F. within the regenerator before being introduced to the incinerator. The main problem with regenerators is that contaminated fumes are left within the regenerative bed when flow through the system is reversed and the bed is switched from the preheating mode to the exhaust mode. There is a risk that these contaminants may be emitted into the atmosphere with incinerator exhaust.
2. Description of the Prior Art
The prior art has generally addressed the problem of residual contaminants by including a purging means with the incinerator to force contaminated fumes from the bed while the bed is between preheating and exhaust cycles. For example, U.S. Pat. No. 3,870,474 to Houston provides a purging means for a system having three regenerators. A first regenerator preheats contaminated fumes prior to incineration while a second regenerator receives and extracts heat from products of incineration. A third regenerator at the same time receives a purge of treated or purified air to force any untreated or contaminated fumes from the regenerator into the incineration chamber. In another form, this system has two regenerators, and a vacuum surge tank is in fluid communication with each regenerator. When flow in the system is reversed, the vacuum surge tank is placed in fluid communication with the appropriate regenerator by a four-way valve and a surge tank valve, and the contaminants within the regenerator are drawn into the surge tank. The contaminants are then evacuated from the surge tank by a vacuum pump, which places the contaminants back into the contaminant inlet.
There are several problems with the vacuum design. First, the vacuum system presents a risk of emitting untreated, contaminated fumes to the atmosphere when the regenerative cycle in the incinerator is reversed. The four-way valve which controls the flow of incoming contaminants and outgoing exhaust must be in perfect synchronization with the valve which admits contaminants into the surge tank. If the surge tank valve is opened an instant later than the reversal of flow, a small amount of contaminants will be emitted through the vent to the atmosphere. Over extended periods of time, this could amount to substantial volumes of untreated fumes exhausted to the atmosphere.
Second, repeated application of a strong vacuum to the entire system substantially decreases the useful life of various parts of the system, especially the valves. Particularly, the surge tank valve and a flap valve on the exhaust vent would require exceptional durability standards. Finally, the purging means, namely the vacuum surge tank, the surge tank valve and the vacuum pump, present added maintenance requirements and initial installation costs, and they may also be problematic in situations where overall system weight is a concern, such as rooftop installations.
Further regenerative incinerator designs may be seen in U.S. Pat. Nos. 4,874,311; 4,650,414; 4,474,118; 4,454,826; 4,302,426; 3,895,918; 3,634,026; 3,211,534 and 1,940,371. Additionally, a publication by Proctor and Schwartz, Inc., dated 1971, discloses a regenerative air purification system having two regenerators and a purge valve, which opens briefly to flush residual contaminated gas into the purification chamber. The disadvantage with this system is that the flow of incoming contaminated fumes must be completely halted while purging is taking place. This may require fans for the contaminated fumes and the purge gas to be frequently stopped and started, and it may also include further undesirable complications for the upstream system from which the contaminants originate.
It is therefore an object of the present invention to provide a regenerative incinerator having purging means which do not result in emission of untreated contaminants to the atmosphere when the purging means are activated. It is a further object to provide a regenerative incinerator with purging means that are relatively compact, lightweight and suitable for rooftop installations. It is a still further object to provide a regenerative incinerator having purging means which require low maintenance and which may be continuously operated to avoid frequent stops and starts and to avoid placing frequent sudden stresses on the overall system. Finally, it is an object of the present invention to provide a regenerative incinerator with a plenum for thoroughly mixing contaminated gases with purge gas and for introducing the mixture to an incineration chamber in a manner that ensures maximum destructive efficiency of the incinerator system.